For the cashewnut paste, put the ingredients in a mixer and grind till it becomes a smooth thick paste. If needed add more milk for blending.
For the onion tomato mixture, brown the onions, add the tomatoes and stir. Add the rest of the ingredients and cook on a medium flame till the water dries and the oil has separated.
Now put the chicken in a bowl. Add the cashewnut paste, 3 tsp of cream, red chilli powder, turmeric powder, salt to taste, fennel seeds and 3 tsp of cream to the chicken.
Mix it all well and marinate for two hours.
Heat the oil in a pan, add the onion tomato paste and the spring onion stems and stir well.
Mix in the bowl of cream into the pan. Add marinated chicken and stir well again. Cover and cook on a slow flame till done.
Serve hot with naan.